Rotworm

This is the most commonly hunted monster in Tibia and you will never be very far from a rotworm cave. You can buy rotworms from Humgolf in Kazordoon, although you need a drilling license to do so. Also common for training at lower skill levels.

Rotworms move slowly and have no distance attack, so they are not very deadly unless you are surrounded. In large groups they can be dangerous.

A rotworm attacks in melee range.

If you cannot kill them fast or withstand attacks from several rotworms at once, never let yourself get trapped in a corner, as you cannot push rotworms. Really easy to hunt for all Vocations. Druids and Sorcerers can hunt them easily with Snakebite Rod or Wand Of Vortex because these use very little Mana and rotworms drop food so you can constantly regenerate.
Knights and Paladins can hunt them with no great trouble even at 30/30, but low-leveled characters (for example players at level 8 who can't use Exura or Exura Ico yet) should be careful not to get trapped, as rotworms are not pushable. These vocations also often use rotworms for training, but they may quickly become insufficient because of their weak defense.
If you are in Rookgaard, do not hunt them alone without good equipment like Chain Armor, Legion Helmet and a Copper Shield. It also helps to bring parcels (or boxes, while in Rookgaard) with you, since then you can take only one or two at a time by blocking them with objects.. Using Bow or Spears instead of melee is also a good strategy.

Graphic Change

Before the 2006 Summer Update rotworms looked like this:

Loot

With Christmas Update 2009, Lumps of Dirt replaced Legion Helmets, Copper Shields and Katanas, increasing the rarity of all these items on Rookgaard as they are now only available in quests. Legion Helmets more so, in that they are now only dropped by Lost Souls and thus, somewhat bizarrely, a rare item.